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Communicating information by radio

  • US 5,128,669 A
  • Filed: 08/30/1990
  • Issued: 07/07/1992
  • Est. Priority Date: 09/04/1989
  • Status: Expired due to Fees
First Claim
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1. An information system for communicating information by radio between mobile transponders and a fixed station, in which system the station irradiates first and second portions of a path for said transponders by a first beam of microwave energy and a second beam of radio energy respectively, said beams having first and second frequencies respectively, the microwave beam having the first frequency activates each said transponder for communication when that transponder is present within the first portion, information is subsequently communicated from that transponder to the station, and information is communicated to that transponder from the station by the station modulating the second beam, characterized in that said first and second portions overlap, said second frequency is lower than said first frequency, communication of information from each activated transponder to the fixed station is achieved by the activated transponder modulating and reflecting a beam of radio energy with which the station irradiates said second portion, which reflected radio beam has a frequency which is lower than said first frequency, said second beam periodically carries modulation containing information, information is first communicated to the station by any newly enabled transponder in response to reception by that transponder of the modulation containing information, a specific address code is communicated between the station and each newly enabled transponder, and the station subsequently modulates said second beam to communicate further information to each enabled transponder using the specific address code to address the relevant transponder.

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